1. Field of the Invention
This invention relates to scanning systems, more particularly to scanning systems that utilize spatial light modulators.
2. Background of the Invention
Scanning systems have many different applications, from photocopying to infrared imaging systems. Most scanning systems, such as forward-looking infrared (FLIR) systems, use a spinning mirror that "throws" a part of the image to a detector at any given time. The use of this mirror causes some problems, such as large size, weight, sensitivity to vibration, and power requirements. The mirror must have some type of driver, such as a motor or a coil. This results in even more volume, weight and power needs.
The spinning mirror does solve one problem. Infrared radiation has a longer wavelength than visible light. It is hard to use a small reflective surface, such as a reflective cell of a spatial light modulator array, with such a wavelength. Diffraction effects, where the light is "bounced" in all different directions, result in high interference between the cells and the detector does not receive an accurate amount of radiation that it can convert into any type of useful image. A similar problem exists in other applications, such as photocopying, where the image must be readable.
It is desirable to use spatial light modulators with such a system in place of the spinning mirror, or other scanning techniques. This would reduce the size of the package, the weight of the system, and the power requirements, and increase mechanical robustness. One candidate for a spatial light modulator might be the deformable mirror devices (DMD) that consist of individual reflective elements that can be deflected over an air gap by an electrode, that are addressed by fast CMOS circuitry. However, a preferred candidate would be the membrane DMD, which has less diffraction problems than other presently available types of DMDs. The membrane DMD is manufactured by placing a metal membrane over a spacer layer, under which lay the electrodes. As an electrode is addressed, the membrane "deforms" at the point of the membrane that was directly above the addressed electrode.
Using a membrane, which acts as a large mirror, the diffraction effects brought on by a spatial light modulators' usually small cell size would be eliminated.